Such devices and processes for the embossing of fine structures can be used for example to produce lengths of film with optical diffraction structures such as holograms, diffraction gratings, etc. at low cost.
Processes according to CH-PS (Swiss Patent) 530 018 are known to emboss the optical diffraction structures into the lengths of film by means of a heated, endless, band-shaped embossing matrix.
An embossing device known from U.S. Pat. No. 4,773,718 is equipped with a rotating embossing cylinder which bears an embossing matrix on its circumference and with a counter-pressure cylinder rolling against the embossing cylinder. The length of film is guided between the two cylinders and is pressed against an embossing matrix by means of the smooth counter-pressure cylinder. With each rotation of the embossing cylinder, the raised structures of the embossing matrix are embossed into the length of film whereby the advancing speed of the length of film is equal to the peripheral velocity of the embossing matrix. Motifs follow each other on the embossing matrix at a predetermined motif interval which is an integral divisor of the circumference of the embossing cylinder. For a different motif interval an embossing cylinder with the corresponding circumference is required.
A "POLYESTER EMBOSSING MACHINE" is known from a printed document of Global Images Inc., 509 Madison Avenue, New York, NY 10022, USA under reference number DP 506 and is equipped with an embossing cylinder between two counterpressure cylinders, whereby the length of film is guided twice to the embossing cylinder via a loop in the film to be embossed. The length of the loop is determined by the circumference of the embossing cylinder. The embossed length of film has segments following each other which were embossed alternately under one of the two counterpressure cylinders. The peripheral surface of one-half of the embossing cylinder serves as a support of the embossing matrix. The other half of the embossing cylinder surface is made in form of a recess in which a mechanical mechanism is installed to clamp the embossing matrix. This arrangement makes it possible to replace the embossing matrix rapidly, but this is at the expense of a poor utilization of the embossing cylinder.
A stamping device with a compensating system serving to catch the continuously fed and removed length of film and which periodically enables the length of film to stop briefly under the stamp is known from EP 244 348.
DE-OS 34 45 012 describes a multi-color printing machine. The machine has a pressure cylinder with one or two printing plates for each color which produces motifs at any desired motif interval on a length of paper. The length of each printing plate is an integral multiple of the motif interval. The printing cylinder is provided with two locations offset by precisely 180.degree. to load the identical rigid printing plates. The circumference of the printing cylinder is considerably greater than twice the length of a printing plate. The length of paper is guided twice over a preset loop to the same printing cylinder to be imprinted by means of two counterpressure cylinders offset by 180.degree.. Between the end of one printing plate and the beginning of the other, the contact between the two printing plates and the length of paper moving at constant speed is briefly interrupted. During that interruption a preset advance of the paper length is achieved through the lowering of the angular velocity of the printing cylinder, whereby an aligning of the printing plate under the second counterpressure cylinder with the as yet unprinted interval between the motifs already printed on the paper length under the first counterpressure cylinder takes place.
It is an object of the instant invention to provide a device and process for economical embossing of fine structures into a length of film, whereby said device utilizes the circumference of an embossing cylinder more efficiently and whereby a preset motif interval between embossed motifs is independent of the circumference of the embossing cylinder.